Solar energy is one of the popular and well known renewable source to produce clean energy. At present there are various means and methods to convert energy from solar radiation into other usable forms of energy such as heat, mechanical work and/or electricity. Majority of such systems are basically designed using Photovoltaic (PV), Concentrating Solar Power (CSP) (Thermal), Concentrating Photovoltaic (CPV) or Concentrating Hybrid Thermo-Photovoltaic (CHTPV) systems. Since the present invention relates to the CSP, CPV and CHTPV class of systems, some of the existing patents in the same field of invention are listed below as reference:
Patent Application/Date ofPublication No.Inventor (s)PublicationPCT/IL00/00372Avi Brenmiller, Menashe11 Jan. 2001WO 01/02780 A1Barkai, Eli MandelbergPCT/IT02/00360Mauro Giuseppe Gianuzzi,27 Dec. 2002WO 02/103256 A1Adio, Meliozzi, EttoreDiego Prischich, CarloRubbia, Mauro VignoliU.S. Ser. No.Paul Fraser, Terry Smith,13 Dec. 201213/422,353Rocco Luongo, JustinUS 2012/0312017 A1Thurgood, Trent, Wetherbee,Raphel Milleret, AllenPeterson, John EdwardAugenblick, Scott McCallum,Ian Williford, Ray Erbeznik,Ben Gyori, Patrcik Fox,Harry McVicker, Tina DaleU.S. Ser. No.David K. Fork,14 Dec. 201011/381,999Stephen J. HorneU.S. Pat. No.7,851,693 B2
A typical CSP system consists of one or more mirrored reflectors that concentrates solar radiation towards an absorber/receiver which produces an intense heat energy. A Heat Transfer Fluid (HTF) is made to circulate through the absorber/receiver to absorb this intense heat energy. The heat energy thus absorbed is used directly to operate a heat driven engine or to produce pressurized steam to power a steam turbine which in turn drives an electric generator to produce electricity. A Sun tracking mechanism is used to follow the movement of Sun throughout the day. Thermal Energy Storage (TES) is optionally used to store excess heat energy collected during day time to produce electricity when direct sunlight is not available. Fossil and/or bio fuel powered systems are optionally integrated with CSP systems in a backup/hybrid mode to extend the duration of energy production in the absence of direct sunlight.
Based on the technology used, CSP systems can be categorized into four types namely Parabolic Trough, Linear Fresnel, Power Tower and Parabolic Dish/Engine. All of these technologies works based on the same basic principle described above.
Though various types of CSP systems are in research and/or commercial use in various parts of the world, major limitations and/or concerns regarding wider usage of such systems are higher cost, huge space requirement, lower conversion efficiency, etc., The following table presents typical operating/evaluating parameters for some of the existing CSP systems1.
Solar to Electrical ConversionOperating Pressure/EfficiencyType of CSPTemperatureIdeal/AverageSystemHTFSteamTypicalAnnualParabolic Trough390° C100 bar25%-26%13%-15%at 370° CPower Tower565° C100-150 bar20%-24%14%- 18%at 540° CDish/Engine-NA--NA-31.4%<20%(max)
A typical CPV system consists of concentrating optics (mirrors or lenses) made out of inexpensive materials such as glass, steel and plastic to focus sunlight onto a relatively small semiconductor area of interconnected high efficiency silicon or multi-junction (MJ) PV cells. The PV cells are capable of converting sunlight directly into direct-current (DC) electricity. This DC electricity can be used directly, stored in a battery and/or converted to alternating-current (AC) electricity for general usage. Unlike regular PV systems, CPV systems require continuous tracking of Sun throughout the day in order to maintain the concentration of sunlight on the cell. This system offers a higher solar to electric conversion efficiency using MJ PV cells (up to 43% under laboratory conditions), but at a higher cost due to the cost of manufacturing of high efficiency MJ PV cells and the complexity of tracking subsystem2.
A typical CHTPV system is a variation of CPV system that incorporates additional mechanism for thermal energy extraction from the heat generated by PV cells in a way similar to CSP systems.
Therefore, primary object of the present invention is to improve the solar to electrical conversion efficiency of the CSP, CPV and CHTPV class of systems which in turn may reduce the cost and space requirements of such systems.